1. Field of the Invention
The present invention relates to wells, abandoned wells, well operations, to methods, apparatus and products for operating wells. In another aspect, the present invention relates to wells, abandoned wells, abandoning wells, to methods, apparatus and products for abandoning wells. In even another aspect, the present invention relates wells, plugged wells, plugging wells, and to methods, apparatus and products for plugging abandoned wells. In still another aspect, the present invention relates wells, treated wells, treating wells, and to methods, apparatus and products for treating abandoned wells.
2. Brief Description of the Related Art
Wells of various types after their useful lives are shut down and usually permanently plugged for a variety of reasons. For example, wells employed in the production of oil and gas are usually abandoned because they reach the end of their useful life or they become damaged beyond repair.
Various jurisdictions in the oil producing regions of certain countries require that abandoned wells be plugged to protect safety and environmental interests, for example, to protect aquifers and the above surface environment.
Wells are most commonly plugged with Portland cement, although a number of alternative materials have been proposed and are less commonly utilized. Generally, a well is plugged by pouring Portland cement into the wellbore, and curing the cement in situ.
It will be appreciated that it would be most uneconomic to attempt to completely fill the well bore with cement. Therefore, it has become widely known to inject cement into the well in such a way that only the potential producing zones are blocked off. These potential producing zones were abandoned due to the fact that they were not commercially viable; however, for ecological and liability reasons, it is necessary that these zones be plugged to stop seepage, contamination, and communication between zones. The potential producing zones may produce oil, natural gas, various forms of other hydrocarbons, salt water and natural water. It will be appreciated that in any one well bore, the potential producing zones may be widely spaced apart; some may be producing a small amount of oil, others natural gas, while others are producing water, etc.
Ordinary drilling mud fills the well bore in the regions between the cement plugs. For the cement plugs to be effective, they must be properly located at the producing zones and must extend a certain minimum distance, say 50 feet, above and below the producing zone thereby to reduce the possibility of seepage.
Formulation of Portland cement in the field is largely a product of trial and error by field personnel to meet irregularities in the cementing composition and the downhole environment. Cement quality control is difficult to achieve under such conditions. As a result, Portland cement cured in situ can exhibit cracking, shrinking, or poor adhesion to wellbore tubulars. An imperfect Portland cement plug can enable undesirable fluid flow through the wellbore via leaks along or through the cement.
It will be appreciated that the well bore is filled from top to bottom with a fluid material commonly termed “drilling mud”. Thus, the regions between the various plugs in the well bore will be filled with drilling mud.
On such method for plugging an abandoned well is taught in U.S. Pat. No. 4,043,394, and while dated, is fairly descriptive of current methods, and is as follows.
1. Government approval to plug the abandoned well is obtained including the specified intervals to plug off the potential producing zones.
2. The drill pipe is lowered downwardly into the well until its lower end is somewhat below the bottom of where the first cement plug is to be located. (The position of the lowermost producing zone is known from information derived from the well logging operation).
3. The cement volume is calculated having regard to the interval or length of the cement plug to be placed across the zone or formation, the well bore diameter and the drill stem dimensions. The reason why the drill stem dimensions are of significance is that after the cement has been injected the drill stem or drill pipe must be lifted out of the cement and thus the level of the cement will drop by several feet depending on the displacement of the drill stem including the length of drill stem which is lifted out of the cement. Thus, this factor must be taken into account to ensure that the producing zone is properly plugged. In addition, an extra quantity of cement, nominally 20% above that calculated as described above, is included to provide a “safety factor”.
4. Cement is then pumped down the drill pipe and exits through its lower end and then passes up the well bore to a point sufficiently high so that it will cover the zone required to be plugged as well as providing for an adequate degree of “safety factor” after the drill pipe has been lifted above the cement.
5. The drill pipe is then raised upwardly to a point above the top of the cement plug. Then, an eight hour waiting period is provided to allow the cement plug to harden sufficiently as to support at least a portion of the weight of the drill pipe. The drill pipe is then slowly lowered downwardly until it contacts the hardened cement. This procedure enables the plugging crew to determine by “feel” the exact position of the top of the cement plug. The elevation of the top of the plug is recorded and compared with the base log data to ensure that the cement plug is at the proper elevation. However, if an error has been made in calculating the volume of cement, or if some of the cement has spread into the producing zone, the plug may be too low, in which event, additional cement will have to be pumped into the drill hole and a further eight hour waiting period provided in order to allow the cement to harden and the location of the top of the plug located as described above.
6. Assuming the lowermost plug is found to be at the correct depth, the drill pipe is pulled up to a position adjacent the bottom of where the next plug is to be located and the procedure described above is repeated.
A number of patents and patent applications are directed to plugging abandoned wells, the following of which are only a small few.
U.S. Pat. No. 4,043,394, issued Aug. 23, 1977 to Campbell, discloses that in order to plug off potential producing zones in an abandoned well, cement is injected at the appropriate level in an amount estimated to be sufficient to seal off the zone. A selected portion of the cement, treated with a radioactive tracer, is injected to provide a layer of treated cement at the top of the wet cement plug and a probe or logging tool is thereafter used to locate the position of the top of the plug with the probe output being recorded graphically to provide a record of the position of the plug top.
U.S. Pat. No. 4,730,675, issued Mar. 15, 1988 to Wygant, discloses a method of plugging an abandoned well with a polymer gel, in which an abandoned well penetrating a subterranean formation is plugged using a gel comprising a high molecular weight, water-soluble carboxylate-containing polymer and a chromic carboxylate complex crosslinking agent.
U.S. Pat. No. 5,343,952, issued Sep. 6, 1994 to Cowan et al., discloses a method for preventing zonal communication or migration of fluids, in a well to be abandoned, by placement of a cement plug comprising a cementitious component, an activator and water.
U.S. Pat. No. 6,098,712, issued Aug. 8, 2000, and U.S. Pat. No. 6,750,179, issued Jun. 15, 2004, both to Burts, Jr., both disclose a well plug additive, well plug treatment fluid made therefrom, and method of plugging a well. The well plug additive includes a dry mixture of water soluble crosslinkable polymer, a crosslinking agent, and a reinforcing material of fibers and/or comminuted plant materials. The method of forming a well plug fluid includes contacting the additive with water or an aqueous solution, with a method of plugging the well further including the step of injecting the fluid into the wellbore.
U.S. Pat. No. 6,374,915 issued Apr. 23, 2002 to Andrews, discloses processes and apparatus for sealing abandoned well bores which includes includes a hopper for dispensing comminuted well bore packing material such as a bentonite clay onto an inclined screening surface which removes undesired fine materials. A chute for collecting material flowing off of the screening surface and directing the same into the well bore is generally funnel shaped. The apparatus includes an eccentric vibrating mechanism for vibrating the inclined screening surface to remove the undesired fine materials.
U.S. Pat. No. 6,715,543, issued Apr. 6, 2004 to Svindland, discloses a particulate matter plug that is placed along all or portions of a well to be permanently or temporarily abandoned, the plug being arranged to hinder/reduce fluid flow to surface. The plug consists of a mass of particulate matter composed of naturally occurring and/or synthetically produced granular matter, including gravel, sand, silt, clay and a mixture of these, and preferably of a poorly sorted mass of particulate matter. The granular particulate matter having average particle diameters included in the statistical range of variation of the mass is comprised of particles with an average particle diameter > 1/256 millimeters, thus comprising approximately ⅔ of all particles in the mass.
U.S. Patent Application Publication No. 2004/0020651, published Feb. 5, 2004, by Burts, III, discloses a well plug additive, well plug treatment fluid made therefrom, and method of plugging a well. For well plug treatment to plug an abandoned well, the well plug additive includes a dry mixture of water soluble crosslinkable polymer, a crosslinking agent, and filter aid, and optionally, a reinforcing material preferably of fibers and/or comminuted plant materials. The method of forming a well plug fluid includes contacting the additive with water or an aqueous solution, with a method of plugging the well further including the step of injecting the fluid into the wellbore.
U.S. Pat. No. 6,767,398, issued Jul. 27, 2004 to Trato, discloses cementitious compositions and cementitious slurries for permanently plugging abandoned wells and processes and methods therefor. A dry cementitious composition which when slurried with water produces an economical hydraulic cementitious slurry for closing abandoned wells. The dry cementitious composition is a cement/CKD blend as the major component with a weight ratio of parts cement to parts of CKD between about 2/3 and about 3/1. Hydraulic cementitious slurries when cured can produce hard cementitious bodies which will meet or exceed the API specification for a competent hard plug. A process for blending the cement and CKD during transit from the cement source to the off-load site without requiring further blending after off-loading. Methods are provided for determining the formulation having the cheapest cost per unit volume of hydraulic cementitious slurry thereby enabling competitive quotes based on cf of hydraulic cementitious slurry required.
In spite of the advances in the prior art, conventional cement systems suffer from a 6 hour safety margin to dump the slurry; long set times; low shear bond values; long cement lengths, and long wait on cement (WOC) times causing high expense.
Thus, there still exists a need in the art for improved methods, apparatus and products for abandoning wells.
There also exists a need in the art for improved methods, apparatus and products for plugging abandoned wells.